Particularly in automotive applications, box sections such as main frame rails are subjected to considerable stress forces where cross members are bolted to the rails. For example, when engine cradles are bolted to main frame rails they produce joints that are susceptible to durability cracking over time. In addition, the bolts which hold such components in place may loosen due to vibration at the joint. Moreover, conventional structures create a "noise path" which extends from the vehicle wheels and engine through the frame and into the passenger compartment.
As will be appreciated by those skilled in the art, in order to bolt a heavy component to the side of a rail section it is necessary to create a reinforced region or support structure at the site of attachment of the bolt. One approach which is used in the art is to provide a stamped bulkhead which supports a metal bushing. The bulkhead generally has three flange portions which are spot welded to the rail C-section. More specifically, the stamped bulkhead has a wall portion that extends from one wall of the rail section to the opposite wall or cap. Thus, the bulkhead forms a partition in the channel or cavity defined by the rail. In order to secure this wall portion in place, the bulkhead has three surfaces or flanges that are perpendicular to the bulkhead wall portion; that is, the bulkhead is in essence a shallow rectangular box that is open on one side. These three surfaces mate with the inner surfaces of the rail and are spot welded in place.
In order to utilize the bulkhead as a support for the cross structure which is attached thereto, it is designed to position a metal bushing that is spot welded to the bulkhead stamping. A bolt then passes through the bushing and secures the cross structure to the rail at the bulkhead-reinforced region. This conventional approach will be more fully illustrated hereinafter.
While the conventional bulkhead design does serve to reinforce the rail section at the attachment site of the cross member, it generally requires large gauge bushings and stampings and can actually increase unwanted vibration and noise. Moreover, the through-bolt, bushing, metal stamping and rail section essentially perform as discrete elements more than a unitary, integral reinforcement structure. This results not only in the above-mentioned increase in vibration and noise, but also fails to provide full reinforcement of the rail, resulting in metal fatigue at the joint and, in particular, at weld locations.
The present inventor has developed a number of approaches to the reinforcement of hollow metal parts such as: a reinforcing beam for a vehicle door which comprises an open channel-shaped metal member having a longitudinal cavity which is filled with a thermoset or thermoplastic resin-based material; a hollow torsion bar cut to length and charged with a resin-based material; a precast reinforcement insert for structural members which is formed of a plurality of pellets containing a thermoset resin with a blowing agent, the precast member being expanded and cured in place in the structural member; a composite door beam which has a resin-based core that occupies not more than one-third of the bore of a metal tube; a hollow laminate beam characterized by high stiffness-to-mass ratio and having an outer portion which is separated from an inner tube by a thin layer of structural foam; an I-beam reinforcement member which comprises a preformed structural insert having an external foam which is then inserted into a hollow structural member; and a metal w-shaped bracket which serves as a carrier for an expandable resin which is foamed in place in a hollow section.
None of these prior approaches, however, deal specifically with solving the problems associated with conventional reinforcing bulkheads in rail sections at cross member attachment sites. The present invention solves many of the problems inherent in the prior art.
It is an object of the present invention to provide a reinforced hollow metal structure which incorporates a bushing and a stamping in a bulkhead structure in a manner in which the components of the bulkhead work together as an integral unit with the reinforced structure.
It is a further object of the invention to provide a reinforced metal box section which provides greater strength to the section without significantly increasing vibration and noise transmission levels.
It is a further object of the present invention to provide a reinforced frame rail section at the attachment of a cross member such as an engine cradle in a manner in which stress forces are distributed over a region of the reinforced rail rather than at the discrete welds and in which noise and vibration are dampened.
These and other objects and advantages of the invention will be more fully appreciated in accordance with the detailed description of the preferred embodiments of the invention and the drawings.